The present invention relates to a polishing apparatus for polishing a plate-like article such as a semiconductor wafer.
With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine and, as a result, spaces between wiring patterns have also been decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography or the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to an exceptionally high degree of surface flatness. To accomplish such a high degree of surface flatness, it has become common to use a polishing apparatus known as xe2x80x9cCMPxe2x80x9d or xe2x80x9cChemical Mechanical Polisherxe2x80x9d.
FIG. 12 shows a polishing apparatus of this type. The apparatus includes a polishing table 102 provided with a polishing cloth 100 on its upper surface, a wafer carrier 104 for carrying a semiconductor wafer W to be polished and an abrasive liquid supply nozzle 106 for supplying an abrasive liquid to the polishing cloth 100. In a polishing operation, a wafer W is held on a lower surface of a wafer carrier 104 to be brought into contact with a surface (polishing surface) of the polishing cloth 100 which is provided on the polishing table 102, with the wafer carrier 104 and the polishing table 102 being rotated about their respective axes. Simultaneously, the abrasive liquid nozzle 106 supplies the polishing cloth 100 with an abrasive liquid consisting of, for example, an alkaline slurry containing abrasive particles such as silica which effects polishing of the semiconductor wafer chemically and mechanically.
The polishing apparatus is also generally provided with a dresser tool 108 which is employed to normalize the polishing surface of the polishing cloth either during or after polishing of a semiconductor wafer. When brought into contact with the polishing surface of the polishing cloth 100, the dresser tool 108 is rotated so as to remove any accumulated abrasive particles and debris and planarize the polishing surface. The wafer carrier 104 and the dressing tool 108 are pivotably supported on struts (not shown) positioned adjacent to and radially outside the polishing table 102, so as to enable each unit to be moved between a work position shown in FIG. 11 and a rest position radially outside the polishing table 102.
The polishing surface of the polishing table 102 is subject to a decrease in rotational movement the closer it is to the center of rotation. Accordingly, during polishing, a semiconductor wafer is brought into contact only with a polishing surface remote from the center axis, thus making it necessary for a diameter of a polishing table to be in excess of twice that of a wafer to be polished. Consequently, a large polishing apparatus must be employed whereby production and installation costs increase.
In an attempt to overcome this problem, there has been employed a polishing apparatus in which a polishing table having a polishing surface is driven in such a manner as to generate a circulatory translational motion thereof in which the polishing table is rotated about an axis spaced away from and parallel to the central axis of the polishing table without any change in orientation of the polishing table, whereby every point on the polishing surface is caused to describe a substantially identical locus, i.e., a circle. The motion of the polishing surface relative to a surface of a semiconductor wafer enables the polishing surface to polish the wafer surface uniformly at all the points of the polishing surface. Consequently, this enables a small diameter polishing surface of a polishing table to be employed having a diameter which is generally equal to that of a semiconductor wafer and is able to polish the semiconductor wafer appropriately.
However, the reduced size of the polishing table gives rise to the following problems. Firstly, the work positions of a dresser tool and a wafer carrier, which units are located above the polishing surface of the polishing table, overlap with each other, whereby the possibility of accidental contact and damage increases. In addition, following completion of a polishing operation, the wafer carrier must be raised to separate a polished wafer from the polishing surface of the polishing table. However, the existence of an abrasive liquid between the polished wafer and the polishing surface generates surface tension, requiring a relatively large force to be applied in order to separate a polished wafer from the polishing surface. Thus, upon completion of a polishing operation, the wafer carrier is generally first pivoted about its holding strut positioned outside of the polishing table to move the wafer to a position where a potion of the wafer extends radially outwardly from the periphery of the polishing surface of the polishing table, whereby surface tension is decreased prior to raising of the wafer carrier and separation of the polished wafer from the polishing surface. However, the circulatory translational motion applied to the polishing table as stated above, results in a shifting effective center point in the polishing table, with the peripheral edge of the polishing table thus becoming indeterminate. Accordingly, if the wafer carrier is, as stated above, moved to a predetermined position before being lifted from the polishing surface, the actual area of the wafer which is in contact with the polishing surface is indefinite, as is the surface tension acting between the wafer and the polishing surface. As a result, it becomes difficult to effectively separate a polished wafer from a polishing surface, and the likelihood of inappropriate movement and consequential damage to the wafer increases.
The present invention aims to solve the problems stated above.
According to the present invention, a polishing apparatus comprises a polishing table having a polishing surface, a carrier for carrying a plate-like member such as a semiconductor wafer and bringing the plate-like member into contact with the polishing surface, and a dresser including a dressing tool adapted to be brought into contact with the polishing surface to dress or normalize the polishing surface. The carrier is movable along a first path between a work position for bringing the platelike member into contact with the polishing surface and a rest position located radially outside the polishing surface, and the dresser is movable along a second path between a work position and a rest position. The second path and the first path have a common overlapping area.
The polishing apparatus further comprises a contact prevention means for preventing the carrier and the dresser from coming into contact with each other during movement along the stated first and second paths.
The contact prevention means may be designed so as to prevent the carrier and the dresser from entering simultaneously any overlapping area.
The polishing apparatus may further comprise means for 25 sensing that a carrier and dresser have approached each other beyond a predetermined limit, whereby movement of either or both units is halted.
The carrier and the dresser may be mechanically connected to each other so as to be able to be moved simultaneously along the first and second path, respectively.
According to another aspect of the present invention, a polishing apparatus comprises a polishing table having a polishing surface, a carrier for carrying a plate-like member such as a semiconductor wafer and bringing the plate-like member into contact with the polishing surface to polish a surface of the plate-like member, a circulatory translational motion mechanism for generating a relative circulatory translational motion between the polishing table and the carrier while maintaining constant contact of the plate-like member with the polishing surface, and an actuator for moving the carrier relative to the polishing surface, to bring the plate-like member into a condition where a predetermined area of the surface of the plate-like member extends beyond a peripheral edge of the polishing surface. Incidentally, the term xe2x80x9ccirculatory translational motionxe2x80x9d noted above is defined as xe2x80x9ca motion wherein every point on an article moves along closed paths in parallel with each other. The closed path may be in the form of, for example, a circle, an ellipse and a polygon. Accordingly, it should be understood that the xe2x80x9crelative circulatory translational motionxe2x80x9d noted above causes every point on the polishing surface to describe a substantially identical locus with respect to the plate-like member.
The polishing apparatus may comprise means for halting the said relative circulatory translational motion in such a state that the plate-like member has a predetermined orientation at a predetermined position relative to the polishing surface. The circulatory translational motion means generates a circulatory translational motion of the polishing table while the carrier is positioned at a predetermined position to keep the plate-like member stationary. The polishing apparatus may include a sensor positioned adjacent to the polishing table for sensing that a predetermined reference point on the polishing table has passed the sensor whereby a signal is emitted, in response to which the circulatory translational motion of the the polishing table is halted by the halting means once the table reaches a predetermined position relative to the emission of the sensor signal.